Multiple ion beam type double focusing mass spectrometer

ABSTRACT

A multiple ion beam type double focusing mass spectrometer designed to control ion beams from a plurality of ion sources so as to form a single beam. The single ion beam is introduced into an electric field while the accelerating voltages or electric field intensity is varied stepwise so that by means of the energy dispersion effect of said electric field, the respective ion beams accelerated at different accelerating voltages are repeatedly and sequentially introduced into a magnetic field. At the output side of the magnetic detector, an ion detector detects said repeatedly and sequentially introduced ion beams and converts them into time shared signals.

United States Patent Naito 1 May 27, 1975 [54] MULTIPLE [ON BEAM TYPEDOUBLE 3,689,764 9/1972 Green et al. 250/296 F C S MASS SPECTROMETER3,796,872 3/1974 Merren 250/285 [75} Inventor: Motohiro Naito, Akishima,Japan Primary Examiner james Lawrence [73] Assignee: Nihon DenshiKabushiki Kaisha, Assistant Examiner-B. C. Anderson Tokyo, JapanAttorney, Agent, or FirmWebb, Burden, Robinson 8L [22] Filed: Dec. 18,1973 Webb 1 1 pp 425,923 [57 ABSTRACT A multiple ion beam type doublefocusing mass spec- [30] Foreign Application Priority Data trometerdesigned to control ion beams from a plural- Dec. 18, 1972 Japan47-12694? Juices as form a Single beam The gle ion beam is introducedinto an electric field while [52] CL 5 250/283; 250/296 the acceleratingvoltages or electric field intensity is 511 1m. (1. n01 j 391/34 variedStepwise so that by means of the energy disper- [58] Field of Search U33 285, 295 296, sion effect of said electric field, the respective ion250/297, 299 beams accelerated at different accelerating voltages arerepeatedly and sequentially introduced into a mag- [56] References Citednetic field. At the output side of the magnetic detec- UNITED STATESPATENTS tor, an ion detector detects said repeatedly and se- 2 45 7,1960B b k t l 50/296 quentially introduced ion beams and converts them ru aere a 3,233,099 2/1966 Berry er al 250/296 mm mm Shared Slgnals'3,475.604 10/1969 Noda et a1. 250/295 10 Claims, 5 Drawing Figuresncrazxnrme v 9 VOL T465 .7

PM/ER SOURCE 8 516N741, I

Ema/Mme CON TROL I 2 Puts:

\ 1 25 Gin/ERA ml! 23 10 1M Mum sol/kc: .s'ouRcz .3001? c: i sue/v41.

[ji T- a PROCEJJ'OR l u 11 3 i r l canRrcr/we M I P0: AMPLIFIER 22 l GinEmma I 1 PATENTED MAY 2 7 ms SHEET (Sec) 6 king l MULTIPLE ION BEAM TYPEDOUBLE FOCUSING MASS SPECTROMETER BACKGROUND OF THE INVENTION Thisinvention relates to a mass spectrometer and more particularly to amultiple ion beam double focusing mass spectrometer for analyzing aplurality of ion beams in a single mass spectrometer unit so as toobtain time shared signals.

Conventional multiple ion beam type mass spectrometers are usuallyprovided with deflection plates for forming periodic ion beams. Theperiodic ion beams are directed to the mass spectrometer proper anddetected as time shared multiple signals. Finally, the multiple signalsare separated by a signal processing device to obtain a plurality ofmass spectra.

With such an apparatus, since the ion beams emitted by the ion sourceare required to be either completely on or off, deflection pulses havingvery high potentials must be applied to achieve sufficient deflection.These deflection pulses, since they subject the ion beams to high energydispersion, impair the resolution of the mass spectrometer considerably.Also, as the energy range of the ions passing through the normally verynarrow indicent slit of the apparatus is limited, the flow rate of theion beams directed through the mass spectrometer is consequentlydecreased and this again lowers the sensitivity of the apparatus. Thereis also a difference in the degree of deflection of the ion beam emittedfrom the respective ion sources. As a result, the dispersion, aberrationand intensity of the individual ion beams emitted from the ion sourcesdiffer from each other which adversely affects the analyzing precisionof the apparatus. The resolution is further impaired as the ion beamsprocessed and already proceeding in particular directions are subjectedto unfavorable deflection owing to the effects of the rise and fall timeof the deflection pulses which produce transient variations in theelectric field. Even ifa deflection is produced in the longitudinaldirection of the slit, assuming that a troidal electric field is beingapplied, a negative effect on the resolution would be virtuallyunavoidable.

SUMMARY OF THE INVENTION The purpose of this invention is to provide aninnovative multiple ion beam type double focusing mass spectrometer foranalyzing a plurality of ion beams using only a single instrument whileat the same time being able to obtain time shared or spliced multiplesignals.

Briefly, according to this invention, ion beams from separate ion beamsources are directed along a common line to the electrostatic analyzerof a double focusing mass spectrometer. Each ion source is provided withan accelerating field controlled by an accelerating voltage source. Ionbeam pulses from at least one of the plurality of beams areintermittently passed from the electrostatic analyzer to the magneticanalyzer because the power supply for the accelerating voltage of thation source and/or the power supply for the electrostatic analyzer arecontrolled to vary the ratio of the accelerating voltage and theelectric field of the electrostatic analyzer such that the ions fromthat ion source have the range of energies to pass through theelectrostatic analyzer and the slit in the baffle following theelectrostatic analyzer only during spaced periodic intervals.

According to one embodiment, ion beam pulses from each of the pluralityof ion beam sources are sequentially passed to the magnetic analyzer adseriatim. In this embodiment, the ratio of accelerating voltage for eachion source and the electrostatic field of the electrostatic analyzer areadjusted such that only the ions from one source at a time have therange of energies enabling them to pass through the electrostaticanalyzer and the slit in the baffle following the electrostaticanalyzer.

In another embodiment of this invention, the respective acceleratingvoltages supplied to a plurality of ion sources are sequentially variedso that each accelerating voltage is periodically returned to areference level for a given pulse duration. The ion beams emitted fromthe ion sources are accelerated according to the accelerating voltagealigned along a common path, to pass through the entry slit of theelectrostatic analyzer. The intensity of the electric field of theelectrostatic analyzer is fixed at a level whereby only beamsaccelerated by the reference accelerating voltage can travel the commonpath and in repeated sequence, be guided into the focusing magneticfield of the magnetic analyzer. The ion beams are detected and amplifiedby an electron multiplier. They provide a time shared or splicedmultiple signal in the detector corresponding to the beam passed throughthe electrostatic analyzer. The electric field of the electrostaticanalyzer has a further purpose to correct ion energy aberrations for anyof the individual ion beams. In a specific embodiment of this invention,an apparatus is designed so that the ion beams emitted from a pluralityof ion sources are each accelerated by voltages of differing values anddirected into a common path. The ion beams in this case, are guided intothe electric field of the electrostatic analyzer which corrects theenergy aberrations of the ions. The intensity of the electric field isvaried in a repeated sequence so that only one ion beam accelerated byits particular accelerating voltage is directed into the focusingmagnetic field at one time. As a result, time shared multiple signalsare detected in the detector.

In yet another embodiment of this invention an apparatus is designed tofix any one of the accelerating volt ages supplied to the plurality ofion sources at a reference level and vary the remaining voltage orvoltage impulses selecting the pulse width and phase to produce arepeated sequence wherein the varied accelerating voltages are at thereference level. Simultaneously, the intensity of the electric field isaccurately fixed at a level corresponding to the reference acceleratingvoltage that passes into the magnetic analyzer. The ion beam from theion source to which the fixed accelerating voltage is supplied iscontinuously introduced into the focusing magnetic field and the ionbeam or beams from the ion source to which the varied acceleratingvoltage is supplied are introduced into the focusing magnetic fieldeither intermittently or in repeated sequence. Time shared multiplesignals superimposed on the signals resulting from the ion beamsaccelerated by the fixed accelerating voltage are obtained in thedetector.

A preferred feature applicable to an apparatus based on any of thepreviously described three embodiments includes a signal generator forinitiating ion production and for determining the ion production period,repitition frequency and phase of the ion source. That is to say, in theapparatus where the accelerating voltage is varied. the ion producingperiod, repetition frequency and phase are determined so that the ionbeams cannot be guided to the detector during the rise and fall time ofthe accelerating voltage. In the case where the intensity of theelectric field of the electrostatic analyzer is varied, the ionproducing period, repitition frequency and phase are determined by thegenerator so that the ion beams cannot be guided to the detector duringthe rise and fall time of the electric field intensity.

In all the above-described embodiments, an electron multiplying tube orFaraday cage may be employed as a detector. The magnetic field is sweptto determine the mass to charge ratio of the ions being studied.

It is also possible to design a multiple ion beam mass spectrometeraccording to this invention, in which the magnetic field is locked andthe accelerating voltage and electric field, which are mutually related,are swept. Since the accelerating voltage or the electric field isvaried by pulses at set intervals, circuit construction becomes rathercomplicated. Should the apparatus be designed so that the sweepingsignal and pulse are superimposed. however, the operation becomes farmore practical.

For a better understanding of the advantages of this invention,reference should be made to the following detailed description based onthe accompanying drawmgs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a block diagram of oneembodiment of the invention;

FIG. 2 shows a block diagram of another embodiment of the invention;

FIG. 3 shows waveforms for explaining the invention; and,

FIGS. 4 and 5 shows the waveforms obtained at the respective detectoroutputs according to the various embodiments of this invention.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, ion sources 1and 2 generate ion beams which are aligned along a common path.Alignment of the beams is caused by deflection electrodes 3 and 4 towhich a constant voltage is applied from power source 5. Thesedeflection electrodes can be dispensed with if accurate superimposing ofthe ion beams is feasible by tilting the ion sources slightly relativeto each other. A correcting electrode 6 eliminates high order aberrationcaused by a slight difference in incident angles of the ion beamsemitted from the ion sources and is an essential component when highresolution mass spectra are required. The correcting electrode requiresonly a small square wave pulse for its effective operation. A controlpulse generator 8 produces a square wave output which is applied to anaccelerating voltage power source 9 and a correcting pulse generator 10.By superimposing mutually phase-reversed square waves from the controlpulse generator 8 on the zero level voltage V produced by theaccelerating voltage power source 9, accelerating voltages as shown inFIGS. 30 and b are applied to the ion sources 1 and 2. Since theaccelerating voltage V,, is sufficiently larger than the amplitude A Vof the square wave, the energy variation A E of the ion beams caused byA V becomes comparatively small. The correcting pulse from thecorrecting pulse generator 10 is synchronized with the control pulsefrom the control pulse generator 8 and the relative phases of theaccelerating voltages are determined so that the ion beams correspondingto the period when the accelerating voltages are at V are properlycorrected. The image at the collector side is focused on the main objectslit in baffle 11. A second slit in baffle 12 limits the ion beamdivergence angle and functions in the same way as the iris of an opticalsystem. The electric field 13 of the double focusing mass spectrometeris basically provided to limit the energy aberration caused by ion beamdispersion and to obtain mass spectra of high resolution. It is designedin conjunction with the focusing magnetic field 14 so as to satisfy themore exacting requirements of the spectroscopes double focusingtechnique. In the double focusing technique, the parameters of theelectrostatic analyzer and the magnetic analyzer are designed to focusions having the same mass to charge ratio but somewhat different initial velocities and directions.

Ion beams emitted from the ion sources 1 and 2 are alternatelyaccelerated by accelerating voltages V and V A V and superimposed so asto form a single ion beam which is introduced into the electric field 13energized by a power source 15. The electric field 13 separates each ionbeam accelerated by V, and A V V utilizing the dispersion effect. Athird baffle having a slit for limiting the dispersion velocity of theion beams is designed to allow only ions of a fixed energy range AE outof the total of ions dispersed throughout the electric field 13, topass. Generally, each ion has a particular energy variation Ac whenionized. Since AE is larger than Ae by a sufficient amount, and therange of energy variations AE due to variations of the acceleratingvoltage AV is larger than the sum of AB and Ae, only ion beams which areaccelerated when the accelerating voltage is V pass through the slit l6and are guided towards the magnetic field l4. Said ion beams are thenfocused by said magnetic field 14 so as to impinge on the center of aterminal slit in baffle 18, thereby passing through to a detector 19such as a Faraday cage where they are detected. The magnetic field 14 isswept by varying the voltage of the magnetic field power source 20 so asto make electrical detection possible of ions of different mass tocharge ratios. The detected signal, which is a time shared multiplepulse having a square waveform, after being detected by the detector 19and amplified by an amplifier 22, is passed to a signal processor 23.The detected signal whose amplitude and base line vary and which carriestwo items of information as shown by the solid line in FIG. 4, issynchronized and separated by a control pulse from the control pulsegenerator 8. Each mass spectrum is then coded and recorded for examplein the memory of the signal processor 23.

Another embodiment of the invention will now be described referringstill to FIG. I. The control pulse generator 8 supplies a control pulsehaving the same phase and waveform as the square wave shown in FIG. 3ato a signal generator 25 thereby initiating ion pro duction. Said signalgenerator supplies ion producing signals alternately during a period Tto the ion sources 1 and 2. Ions are produced only during the period T,which is delayed relative to the rise and fall time of the control pulseby 6T and thus only occur within the period T/2 of the particularcontrol pulse. Since no ions are produced at the rise and fall time ofthe accelerating voltages a and b, unfavorable deflection of the ionbeams in the vicinity of the electric field 13, due to the transientaccelerating voltage variations, is avoided. The processing of the ionbeams is the same as described above.

FIG. 2 illustrates another embodiment of the invention. In the figure,the accelerating voltage power source 9 (the labelling in FIG. 2corresponds with that in FIG. 1) applies accelerating voltages ofdiffering levels to the ion beam sources 1 and 2, so that each ion beamsource emits ions at different energy level. Each ion beam is deflectedby the deflection electrodes 3 and 4 so as to converge them into asingle beam which enters the electric field 13. The control pulsegenerator 8 supplies square wave control pulses to the electric fieldpower source and the signal processor 23. By so doing, the electricfield power source 15 supplies controlled voltages to the electrodesproducing the electric field with the result that the field intensity,which is in synchonism with the energy of the ion beams emitted from therespective ion sources, is repeatedly and sequentially changed inaccordance with the rise and fall time of said control pulses. Theelectric field 13 focuses the ions, corrects the aberration caused bythe differences in the energy levels of the ions, and separates themultiple ion beams produced by the dispersion effect. The pulsed ionbeams from the respective ion sources selectively pass through thedispersion limiting slit and are guided into the magnetic field 14 whichis swept by the magnetic field power source 20. The magnetic field 14also functions so as to focus the ion beams. The ion beams are thendetected by the detector 19 and appear as the signal shown by the solidline in FIG. 4. This detected signal is separated in the signalprocessor in accordance with the control pulse from the control pulsegenerator 8 and recorded in the memory according to the mass spectrum ofthe particular ion beam.

In another embodiment of the invention, a control pulse from the controlpulse generator 8 is applied to the signal generator 25 which controlsion production. Ions are produced only during the period T suitablydelayed in relation to the rise and fall time of the control pulse byBT, and only occur within the period T/Z of the respective controlpulse.

With the embodiment shown in FIG. 1, it is possible to create theaccelerating voltage waveform supplied to each ion source independentlyin synchronization with the control pulse. In FIGS. 3a and b, the riseand fall times of the accelerating voltages coincide with each other.However, it is possible to design an apparatus in which said rise andfall times are timed so that as one accelerating voltage is rising, theother is falling with an appropriate delay and vice versa. In this case,although the multiple signal shown in FIG. 4 can be obtained in thedetector, each plotted signal becomes a time shared pulse which returnsto the base line.

It is also possible to design an apparatus in which one acceleratingvoltage is continually fixed at a specific value while the remainingaccelerating voltages are varied. FIG. 5 shows the resultant detectedsignal obtained by such an apparatus. In this case, since one componentof the signal is time shared and the other is the sum of bothcomponents, it is necessary to subtract the signal component from theadded signal. Processing of the signal components is performed by thesignal processor. If it is necessary to vary the flow rate of the ionbeams from the individual ion sources, the desired effeet can beobtained by changing the time ratio during which the ion beams areguided to the magnetic field.

In a typical application of this invention, a standard sample such asparafluorokerosene is introduced at one ion source and the sample to beexamined is introduced at the other ion source. Since the masschargeratio of the standard sample is normally less than 800, regularlyordered spectra with a correctly known mass number can be obtained atevery l2 to 14 mass numbers. If, however, the sample to be examined hasa mass-charge ratio of more than 800, it will be impossible to verifythe mass spectra by comparing said sample with a standard sample. Inthis case, the sample to be examined is introduced at the first ionsource together with a standard sample, the combined samples are ionizedand the resulting ion beams are accelerated by V At the same time, astandard sample only is introduced at the second ion source and isionized and the resulting ion beams are accelerated by an acceleratingvoltage V larger in value than V Thus, the intensity of the elec tricfield is converted alternately in accord with V and V at intervalssufficiently smaller than any one peak width. Superimposed spectra ofboth samples can be obtained in the detector where the mass spectrumfrom the second ion source appears in the position of greater mass. Inthis case, there is a correlation MN, M V between the mass numbers M andM which are accelerated by V, and V; respectively and arrivesimultaneously at the collector. Now suppose V KV then the value for Kcan be obtained by comparing the known mass peak of the standard samplefrom the first ion source with the known mass peak of the standardsample from the second ion source so that the high mass peak of thesample being examined can be positively determined.

As described above, in this invention, it is possible to deal withmultiple ion beams from a plurality of ion sources and channel them intoa single ion beam. Further, it is possible to obtain mass spectrarelevent to specific ion beams emitted from individual ion sources byusing a single mass spectrometer making possible a wide range ofapplications such as the measurement of mass spectra of the same samplewith different source; measurement of the sample by comparing it with astandard sample; simultaneous measurement of different samples and manyothers.

I claim:

1. In a double focusing mass spectrometer comprising an electrostaticanalyzer with adjustable power supply, a magnetic analyzer withadjustable power supply, at least one baffle with an aperture thereinbetween said electrostatic and magnetic analyzers, an ion detector and aplurality of ion sources,

the improvement comprising means for guiding the plurality of ion beamsemitted from said sources along a common path in a single ion beam tothe electrostatic analyzer,

individually adjustable power supplies for each ion source, adjustingcircuit means associated with at least one of the adjustable powersupplies for adjusting the ratio of the ion source accelerating voltagesand the electric field strength of the electrostatic analyzer, saidadjusting circuit means including a control pulse generator fordirecting the adjusting circuit means for some period of time to passmore than one ion beam to the magnetic analyzer but for that period topass no more than one ion beam from a given source continually to themagnetic analyzer and to pass the ion beam from at least one sourceintermittently to the magnetic analyzer. means associated with at leastone of the adjustable power supplies for sweeping the ratio of theenergy of the ion beams passing the electrostatic analyzer and themagnetic field strength of the magnetic analyzer such that the detectordetects time shared multiple signals indicative of the mass to chargeratios of ions comprising the ion beams passed to the magnetic analyzer.

2. The improvement set forth in claim 1 wherein said adjusting circuitmeans adjusts the ratio of the each ion source accelerating voltage andthe electrostatic field ad seriatim such that ion beams from each ionsource pass in pulses to the magnetic analyzer ad seriatim.

3. The improvement according to claim 2, wherein adjusting circuit meanscomprising means for intermittently bringing the accelerating voltage ofat least one power source to a reference voltage, said reference voltagebeing in the correct ratio with the strength of the electrostatic fieldto pass the ion beam to the magnetic analyzer.

4. The improvement according to claim 3 comprising a signal generatorfor determining the ion forming period, repitition frequency and phasethereof so that the ion beams do not pass through the electric fieldduring the rise and fall times of the accelerating voltages.

5. The improvement according to claim 2 wherein said adjusting circuitmeans comprises means for fixing said ion source accelerating voltagesat mutually different levels and for adjusting the intensity of theelectric field in a repeated sequence so that the ion beams acceleratedby said accelerating voltages are introduced into the magnetic field adseriatim.

6. The improvement according to claim 5 comprising a signal generatorfor determining the ion forming period, repitition frequency and phaseso that the ion beams do not pass through the electric field while theintensity of said electric field is being varied.

7. The improvement set forth in claim I wherein said adjusting circuitmeans adjusts the ratios of each ion source voltage and the electricfield to permit the ion beam from one ion source to be continouslypassed to the magnetic analyzer and the ion beams from at least anotherion source to pass in pulses to the magnetic analyzer.

8. The improvement according to claim 7 wherein the adjusting circuitmeans comprises means for bolding one ion source accelerating voltage ata reference voltage and the strength of the electric field to pass ionsaccelerated through the reference voltage and adjusting the acceleratingvoltages of at least another ion source to the reference voltage.

9. The improvement according to claim 8 comprising a signal generatorfor generating signals for determining the ion forming period of saidion sources, the repitition frequency, and phase thereof relating tosaid adjusting circuit so that the ion beams do not pass through theelectric field during the rise and fall times of the acceleratingvoltages.

10. The improvement set forth in claim 1 comprising a signal processingcircuit in synchronism with said adjusting circuit means for recoveringsignals indicative of the mass spectra of the ion beam from each ionSOUI'C8.

1. In a double focusing mass spectrometer comprising an electrostaticanalyzer with adjustable power supply, a magnetic analyzer withadjustable power supply, at least one baffle with an aperture thereinbetween said electrostatic and magnetic analyzers, an ion detector and aplurality of ion sources, the improvement comprising means for guidingthe plurality of ion beams emitted from said sources along a common pathin a single ion beam to the electrostatic analyzer, individuallyadjustable power supplies for each ion source, adjusting circuit meansassociated with at least one of the adjustable power supplies foradjusting the ratio of the ion source accelerating voltages and theelectric field strength of the electrostatic analyzer, said adjustingcircuit means including a control pulse generator for directing theadjusting circuit means for some period of time to pass more than oneion beam to the magnetic analyzer but for that period to pass no morethan one ion beam from a given source continually to the magneticanalyzer and to pass the ion beam from at least one sourceintermittently to the magnetic analyzer, means associated with at leastone of the adjustable power supplies for sweeping the ratio of theenergy of the ion beams passing the electrostatic analyzer and themagnetic field strength of the magnetic analyzer such that the detectordetects time shared multiple signals indicative of the mass to chargeratios of ions comprising the ion beams passed to the magnetic analyzer.2. The improvement set forth in claim 1 wherein said adjusting circuitmeans adjusts the ratio of the each ion source accelerating voltage andthe electrostatic field ad seriatim such that ion beams from each ionsource pass in pulses to the magnetic analyzer ad seriatim.
 3. Theimprovement according to claim 2, wherein adjusting circuit meanscomprising means for intermittently bringing the accelerating voltage ofat least one power source to a reference voltage, said reference voltagebeing in the correct ratio with the strength of the electrostatic fieldto pass the ion beam to the magnetic analyzer.
 4. The improvementaccording to claim 3 comprising a signal generator for determining theion forming period, repitition frequency and phase thereof so that theion beams do not pass through the electric field during the rise andfall times of the accelerating voltages.
 5. The improvement according toclaim 2 wherein said adjusting circuit means comprises means for fixingsaid ion source accelerating voltages at mutually different levels andfor adjusting the intensity of the electric field in a repeated seqUenceso that the ion beams accelerated by said accelerating voltages areintroduced into the magnetic field ad seriatim.
 6. The improvementaccording to claim 5 comprising a signal generator for determining theion forming period, repitition frequency and phase so that the ion beamsdo not pass through the electric field while the intensity of saidelectric field is being varied.
 7. The improvement set forth in claim 1wherein said adjusting circuit means adjusts the ratios of each ionsource voltage and the electric field to permit the ion beam from oneion source to be continously passed to the magnetic analyzer and the ionbeams from at least another ion source to pass in pulses to the magneticanalyzer.
 8. The improvement according to claim 7 wherein the adjustingcircuit means comprises means for holding one ion source acceleratingvoltage at a reference voltage and the strength of the electric field topass ions accelerated through the reference voltage and adjusting theaccelerating voltages of at least another ion source to the referencevoltage.
 9. The improvement according to claim 8 comprising a signalgenerator for generating signals for determining the ion forming periodof said ion sources, the repitition frequency, and phase thereofrelating to said adjusting circuit so that the ion beams do not passthrough the electric field during the rise and fall times of theaccelerating voltages.
 10. The improvement set forth in claim 1comprising a signal processing circuit in synchronism with saidadjusting circuit means for recovering signals indicative of the massspectra of the ion beam from each ion source.